1. Field of the Invention
The present invention relates generally to disc cartridges, more particularly, to a disc cartridge for keeping a disc-shaped storage medium therein and significantly reducing air resistance therein which is generated by the rotation of the disc-shaped storage medium when the disc cartridge housing disc-shaped storage medium is in operation.
2. Brief Description of the Related Art
There exist two types of disc-shaped storage mediums: One is a storage medium housed in a disc cartridge that is recorded/reproduced in that state. The other is a storage medium that is used without a disc cartridge, like a disc-shaped storage medium shown in FIG. 1. Examples of disc-shaped storage mediums of the latter are CD-DA, CD-R, CD-RW and DVD. The disc D of FIG. 1 has a center hole 1 punched thereon and a clamping area 2 that is formed around the center hole 1. Digital information of audio and video is recorded on a data recording area 3 on one side of poly-Carbonate substrate of 1.2 mm in thickness, and on the other side, information about the disc, e.g., figures or characters are printed.
When the disc D is inserted in a disc driving unit, the disc Disclamped by a clamper 6 around the clamping area 2 of the disc D and then starts to rotate. It is in the interior of the disc driving unit 5 that the disc D rotates.
FIG. 2 shows a disc cartridge 10 for keeping a disc-shaped storage medium therein in such a way that the disc-shaped storage medium is recorded/reproduced in that state. The disc cartridge comprises the interior 11S (shown in FIG. 4) of a housing case 11, where a disc D is kept and rotated; a spindle window 12 which fits with a rotatable spindle (not shown) of a disc driving unit 16 (shown in FIG. 4) and is formed in the center of the housing case 11; a shutter 13 which is slidably attached on one side of the housing case 11 to open and/or close the opening portion of the housing case 11; a gripping slot 14; and an insertion slot 15. The disc D is typically double-sided, i.e., both sides of the disc are used to store digital information.
In order to reproduce the disc D, the disc cartridge 10 keeping the disc D therein is loaded onto a recording/reproducing apparatus. At that time, the shutter 13 is moved so that a pickup (not shown) can read/write information from/to the disc D. It is in the interior 11S of the disc cartridge 10 that the disc D rotates.
The recent trend on high record/reproduction rate of disc-shaped storage mediums demands the increase of the rotational speed of the disc-shaped storage mediums. However, in the case of the disc D housed in the disc cartridge 10, the maximum rotational speed or the speed limit ensuring the stable read/write operation is typically lower than that of the disc requiring no cartridge. This is due to the difference of space in which the disc rotates in normal operation.
Whereas discs requiring no cartridge rotate with a spacing of 10.5 mm from the top and the bottom of the driving unit, as shown in FIG. 3, the discs housed in the housing case in the interior of the case, with a spacing of 4.4 mm from the top and the bottom of the case, as shown in FIG. 4.
Hence, an air flow which is induced by the rotation of the disc D causes the air resistance by which the rotation of the disc in the interior 11S is disturbed. Due to the induced air resistance in the housing case, the maximum operational rotational speed of the disc D in the cartridge 10 is limited to a lower rotational speed than that of the disc of FIG. 1.
To be specific, a high rotational speed of the disc D is not achieved at the initial driving phase because of the air resistance induced by air flows in the interior 11S of the cartridge 10, and thus there are difficulties in achieving a desired high rotational speed of the disc in a desired short period of time. Changing the rotational speed of the disc in operation for maintenance of a constant linear velocity is also disturbed by the air resistance. Moreover, the air resistance may cause disturbance in the rotation of the disc D, resulting in the generation of vibration and noise thereby.